That's not Bitmain, that's a reseller market place. Bitmain itself charges 0.0001125/GH/s. That's not really that important a distinction though.
The biggest difference is that they charge a maintenance fee of $0.0022896/GHS/Day. At the current price, that's BTC0.00018874/month.
Here's a fair comparison:
AMhash = 0.0028 btc/year
Bitmain = 0.0031 btc/year
KNC = 0.0032 btc/year
PBmining = 0.0014 btc/5years
Clearly these hardware manufacturers with massive economies of scale and ultra cheap electricity cannot compete with PBmining.